Process of improving the resistance to corrosion of articles of magnesium and magnesium alloys



l 10 example, the castin latented HQ. 2 1930 UNITED isrATEs mum--or'rlC-a anoLr are: Ami eus'rav smnanor Bmmnnn, mm, aasrenons To 1 e.rannmrmnus'rnm minnensmracnarr, or rnmnonr-omrrm-m, cum

mm, A conrom'rron or emamr raocass or nrrnovme m nmxs'mncn ro connosronor am: MAGNBBIUI ALLOYS ARTICLES 0! IAGHISIUI Ho Drawing. Applicationmed January :0, ms, Serial no. seam, and in Germany I'ebrnary a, mas,

, Thisvinvention relates to a process of improving the resistance tocorrosion f articles I and the like of ma 'nesium and high percenta emagnesium a loys containing] at least 5a out 80% Mg.

Work pieces of high percentage magnesium-alloys frequently containsurface impurities which give rise to an accelerated 'corrosion undercertain conditions.- Thus, for

0 skin formed on the-surirequently contains comesium which may give riseto local attack corrosion. Pressed, rolled or otherwise worli'ed uppieces are also superficia-lly covered with a skin in which are emfaceof cast parts pounds of ma 1 bedded particles of iron and decomposedorganic compounds resulting from the use .of

' tools and lubricants, the presence of which,

I particles, even if only in traces, increas es the actionof corrodingagents, apparently m consequence of local galvanic action.

Now 'we have ascertained that the resistance of the said alloys againstcorrosion may be improved .by treating the a boilin (containing about100 grams .of CrO, per

' liter), for an hour or longer. "B y this treatment anextreinely thintransparent, coating metal pieces wit insoluble in water, containingoxidic chromev compounds and having a yellowish brown hue resembling thecolor of brass-is deposited on the surface of .themetal; 1': i

' The efiect of the surfaoetreatmentcontemplated by the resentinvention-' can-be im- V proved by etching the metal'gpiecesa 'th di-'lute nitric acidlfor example I0% aoi prior. to their treatment withboilin%aqueoujs solutions of dichromates, where y the ?metal pieces arefreed from various superficially adhering impurities, such asfor examplethose arising when the-metal pieces are cast Lthereto.

aqueous solution of dichromates egce tional degree. The modified surfacepro need by the dichromate treatment, fur-- v the'rmore, exhibits theadvantagepus property of durably retaining lacquer coatings applied ,5

Weclaim: A

1. Theprocess of improving the resistance to corrosion of articles'ofmagnesium and magnesium alloys containing at least about 8% magnesium,which comprises treating same with a boiling aqueous=solution of di-\chromate's for about-an hour at least. I

2. The process of improving the re'sistance--- to corrosion of articlesof mum and magnesium alloys containing at least about 80% magnesium,which comprises trea'ting same witha boiling aqueous solution ofdichromates {or about an hour at least; said treatment bein preceded. bya preliminary etching with di lite nitric acid. 3r The process ofimproving the resistance to corrosion of articles of magnesium andmagnesium alloys containing at least about 80% magnesium which comprisestreating the same with a boiling solution consisting of a water-solubledichromate and water, said di-' chromate bein presentin a quantitycorres onding to about 109 grams of CrO, per hter, for about one hour atleast, Slidftreatment being precededby a preliminary etchiin, sandmoulds, and the superficial casting I skin obtained insuch cases isremoved;

The herein described pr ss may be ap- 45 plied towork pie'ces pro needby casting,

- 'rolIin ,die-pressing, any other method.-

.provement of the surface qualities, the resistance of these work-piecesto the corrodfiressure-castin on by H) ing eii'ect of aqueous solutionsis raised to an y virtue of t is imour hands; I e v f i V ADOLF BECK. v

' GUSTAYiSIEBEL.

